Roentgenography frequently requires that intense x-radiation be provided over a relatively short interval of time, for example, one-tenth second or less in the case of an angiogram to prevent blurring of the image due to motion of the blood vessels of a human subject. For radiograms of the human skeleton, longer exposure times can be accommodated so long as the patient can remain stationary. Shorter exposure times require the use of higher intensity radiation for good quality images on the photographic plate since the total incident energy required to produce the image on the photographic plate is approximately the same for both short and long exposure times. A problem arises in that there is a limited intensity of radiation that can be provided by the typical rotating anode target of an X-ray tube because of overheating of the target at the point of impact of an electron beam upon the target. This problem is further intensified by the fact that high resolution radiography requires that the target emit the X-rays from a relatively small spot, typically less than ten square millimeters, thereby increasing the temperature of the target.